It will ask you to sign-in to Facebook and approve the Amazon app.
BEWARE to REVIEW the PRIVACY SETTINGS now, before you proceed, otherwise you may have a lot of hassles.
This app will have control to "spam" your friends about this and other Amazon offers that you redeem, but you can prevent it from doing so, by selecting "Only Me" privacy settings ON THE SAME PAGE that you can approve the app.
When it asks you to approve the Amazon app, pulldown the privacy selections and choose "Only Me" to prevent your friends from being "spammed".
That way, you retain control to post about this and other Amazon deals you redeem, without an app doing it without your control.
Existing Amazon app users can always refer to the Facebook Help for info about controlling your app privacy settings.

The $5 promotional credit will be linked to your Amazon.com account, and automatically applies at checkout on purchases of $25 or more on physical products sold by Amazon.com.

That is it.
You do not have to buy anything today, but you must spend at least $25 on physical products shipped and sold by Amazon before 11:59pm PST on Wednesday, November 21 or the $5 credit will disappear.
If you forgot to select "Only Me" as the privacy settings when you approved the Amazon app, and you want it to stop posting on your wall, here is what you can do.
Follow the instructions on Facebook Help to change the privacy settings for the Amazon app.
Here is how we did it:

You can go to Facebook, click the down-arrow in the very upper-right of the page (next to Home), and select "Privacy Settings".

Scroll down to where it says "Ads, Apps and Websites" and press "Edit Settings"

Do you see the Amazon app? If so, click it.
If not, select "Edit Settings" to the right of "Apps you use" then click the Amazon app.

Look for "Posts on your bahalf" and use the pulldown to select "Only Me"

Go to your Facebook page, and remove or hide any offers that were already posted.